Gaussian
Screen composite for the reduced-resolution Gaussian-splat pass. Draws one full-screen quad sampling the pass color texture (premultiplied alpha) over the scene; the global GL_ONE, GL_ONE_MINUS_SRC_ALPHA blend state completes the over-compositing, so the result matches direct full-resolution rendering up to the resolution of the offscreen target.
The pass framebuffer grows monotonically and can be larger than the rendered area, so loadTexScale maps the unit quad onto only the rendered sub-region of the texture.